1. Field of the Invention
The present invention relates to cooled structures or structural components.
Some constructions require--or will require--refractory structural components capable of supporting long periods of contact with gases at extremely high temperatures, e.g. 1700.degree. to 3400.degree. C.
This in particular applies to combustion chamber walls of combined jet and rocket engines, or to parts of aerodynamic structures of hypersonic space planes, especially the nose tip, leading surfaces of wings and air intake fairings.
2. Prior Art
Walls made of a metallic material with no protective coating would require a considerable amount of cooling by fluid circulation. When the cooling fluid happens to be liquid hydrogen (one of the rocket engine fuels), this would lead to a substantial over-consumption of hydrogen, and a more complicated cooling circuit. A thermally protective coating, such as ceramic, could be formed on the metal walls. However, such a coating may turn out to be insufficiently effective and could, moreover, constitute a hazard in the event of it chipping off.
Despite their refractory nature, walls made of ceramic materials would also require some active cooling, albeit to a lesser extent than metallic walls.
The use of sintered ceramics would be difficult to envisage, owing to their insufficient mechanical resistance, shock resistance and toughness.
This is not the case with composite materials having a refractory matrix (carbon or ceramic), whose thermostructural properties are well known.
Refractory matrix composite materials consist of a fibrous preform made from refractory fibers (carbon fibers or ceramic fibers) densified by a ceramic that constitutes the matrix of the composite material.
The use of refractory matrix composite materials for the manufacture of cooled refractory structures raises a variety of problems.
In particular, it would be preferable, for an enhanced evacuation of the thermal flux, to have the structure made of a heat-conducting material on the side opposite to the one exposed to the high temperatures. But difficulties would then arise with the use of different materials needed to form the wall, on account of their differential expansions, these being considerable at the envisaged service temperatures.
In another approach, involving attempts to form channels or to integrate conduits in the composite for cooling fluid circulation, there would then arise a difficult problem as regards sealing. The integration of conduits in a refractory composite material causes other difficulties that are also connected with differences in the thermal expansion coefficients between the conduits and the refractory composite material.